Field of the Invention
This invention relates to sanding blocks used in the profile sanding of wood. These blocks are shaped and profiled backing blocks. Typically, they provide support for an abrasive-sided sheet or belt as it sands the wood.
Well known commercial uses of these blocks are in traveling belt sanding machines. The belts in these machines are abrasive coated. A work piece is pressed up against the backing block while the moving belt smooths its surface.
Traditional preparation of blocks has included machining, cutting, or otherwise forming, in the block, a reverse profile of the wood to be sanded. Since a different block was required for each distinct shape of wood, the cumbersome, conventional block preparation methods discouraged variety due to the difficulties encountered in replacing the block.
The reverse profile of the wood profile to be sanded is found on one face of the block, known as a pressure face. This face presses against the back of the abrasive sheet or belt as it sands and smooths the working piece to provide moldings, furniture, and the like.
It is known for belts to move at 2500-5000 ft./min. Thus, when the backing block and belt press together a considerable amount of heat is caused by the friction. Friction and heat cause problems including block deterioration, uneven wear, shortening of belt life and contour changes due to block expansion are encountered.
Blocks found described in the art include those of U. S. Pat. No. 4,662,121 which describes blocks with air holes for cooling. These blocks are made of mullite, and are formed from aluminum silicate which must be heated to 1550-1625.degree. C. The belt contacting face of these blocks are machined (or formed mechanically) and highly polished.
U. S. Pat. No. 2,717,422 also describes backing blocks used in wood sanding operations. These blocks have a pressure face liner of a dimensionally stable plastic.
The instant invention provides several advantages over prior art sanding blocks. The phosphate ceramic backing blocks are much easier, faster, and cheaper to make. The simple preparation method of the ceramic block allows blocks to be replaced much more easily.
Since the blocks provided in accordance with the instant invention are made with phosphate ceramic, they have dimensional stability even though a great deal of heat builds up during the sanding operation. Even with this heat build-up, furthermore, these phosphate ceramic blocks also provide good belt life. In addition to this, since the present ceramic backing blocks are dimensionally stable in spite of the heat, it is not mandatory to provide means for cooling the blocks.